1. Field of the Invention
The present invention relates to a liquid application device and an inkjet recording apparatus. Particularly, the present invention relates to a liquid application device, an ink jet recording apparatus each applying liquid to a medium for a certain purpose which is, for example, to promote the aggregation of pigment when recording is carried out by using ink containing the pigment as a coloring material. In addition the present invention relates to a method of controlling the liquid application device.
2. Description of the Related Art
As for an ink jet recording apparatus such as a printer, it is generally known that treatment liquid insolubilizing or coagulating coloring material of ink is used to improve recording quality such as bleeding, density, color tone, offset and the like, and robustness of the image such as waterproof and antiweatherability.
One of methods of applying the treatment liquid to a recording medium is that the treatment liquid is ejected to the recording medium with a recording head in the same manner as the ink is ejected. However, in this method, because mists of treatment liquid are generated by the ejection, it is possible to generate clogging of nozzles caused by the mists of treatment liquid. Moreover, in order to eject the treatment liquid stably form the recording head, many constraints are generated for the viscosity of the treatment liquid, the surface tension, the composition of solution, and the like.
In contrast, a method is known of applying the treatment liquid to the entire recoding medium with rollers. FIG. 34 is a cross sectional view showing a main part of a treatment liquid application mechanism using this method. In this figure, a recording medium 63 is wound, by a press chuck 62, around a platen roller 61 rotated by a motor (not shown). In addition, treatment liquid 65 is contained in a coating unit 64. By means of an agitating and supplying roller 65, the treatment liquid 65 is agitated and supplied to transport and film thinning roller 68. Then, the transport and film thinning rollers 67 and 68 form the treatment liquid 65 into a thin film on a roller surface of an application roller 69. The application roller 69 rotates while pressing onto the recording medium 63 wound around the rotating platen roller 61, and applies the treatment liquid 65 to the surface of the recording medium 63. At the same time, a recording head 70 performs recoding by ejecting ink onto the surface of the recording medium 63 to which the treatment liquid 65 has been applied. As mentioned above, by means of the method of applying the treatment liquid in advance by using the application roller, liquid with relatively high viscosity can be thinly applied without causing mists of treatment liquid to generate, as compared with the method of ejecting the treatment liquid by using the recording head.
In addition, as for a liquid application mechanism which applies application liquid such as treatment liquid to a medium with the rotation of a roller, one described in Japanese Patent Application Publication No. 2002-517341 is known. In Japanese Patent Application Publication No. 2002-517341, a doctor blade contacting with a roller is used to cause coating liquid to be stored between the doctor blade and the roller, and the coating liquid is applied to the roller as the roller rotates. Then, as the roller rotates, the applied coating liquid is transferred and applied to a support medium transferred between this roller and another roller. Likewise, in Japanese Patent Application Laid-open No. Hei 8-72227, described is a liquid application mechanism applying treatment liquid insolubilizing dyestuffs before recording.
In the aforementioned liquid application mechanism, since the application roller is exposed to the air in a state where no fresh treatment liquid is supplied thereto while the application operation is not performed, the treatment liquid remaining on the surface of the application roller is thickened. The longer the application operation is out of service, the larger a degree of increase in viscosity of the treatment liquid becomes. In other words, if a relatively long time passes in a state where the treatment liquid adheres to the application roller, viscosity of the treatment liquid rises due to vaporization of a solvent such as water in the treatment liquid. When the application operation is performed in this state where the viscosity has been increased like this, the rollers cannot rotate well and an appropriate amount of application liquid is not supplied to the roller. Accordingly, the problem arises that application to the recording medium cannot be satisfactorily performed.
Needless to say, the aforementioned problem does not arise only in the application mechanism with the configuration shown in FIG. 34. It is the matter of course that there exist various portions in contact with the treatment liquid between the portion where the treatment liquid is stored and the application roller in the case of the configurations in FIGS. 11, 21, 27, and 30 to be described later. This is the case with most of the configurations which apply the treatment liquid by using the application roller. In these portions in contact with the treatment liquid, the problem arises due to the aforementioned thickening of the treatment liquid. For example, an application mechanism is also known in which the treatment liquid retained in a space formed by causing a part of a liquid retention member to abut on an application roller, is applied to a medium via the application roller. In this mechanism, the treatment liquid, which exists in not only the application roller, but also the liquid retention member and the portion where the retention member abuts on the application roller, also thickens. This sometimes causes the same problem as mentioned above.
In order to solve the aforementioned problem, it is known that application initial operation is performed in advance before an application operation accompanying recording (see Japanese Patent Application Laid-open No. 2002-96452). This indicates that the treatment liquid-application operation is performed without recording medium periodically during a waiting time for the recording operation (namely, during a time not in the application operation). That is, the respective rollers, including the application roller, to which the treatment liquid adheres, are driven to be rotated and the treatment liquid is supplied to the surfaces of these rollers to cause a flow of the treatment liquid. In Japanese Patent Application Laid-open No. 2002-96452, the application initial operation is performed when an apparatus is powered on (apparatus start-up time). The above-mentioned application initial operation circulates the treatment liquid on the surfaces of the application roller and the like, to cause the viscosity of the treatment liquid on the respective rollers to return to a normal value, and to make an application condition be in a state that the application roller is caused to satisfactorily perform the application operation.
In the construction which performs the application initial operation periodically during the waiting time for recording, however, in some cases, particularly, home users are nervous about noise and receive an uncomfortable feeling.
In Japanese Patent Application Laid-open No. 2000-96452, as described above, not only the application initial operation is performed in order to deal with thickening of the treatment liquid during the waiting time for recording in a power-on state, but also the application initial operation is performed just after power is turned on, in order to deal with thickening of the treatment liquid in a power-off state. There is a difference in degrees of sticking of the treatment liquid to the application roller between the case when the power is off for a long time and the case when the power is off for a relative short time. Accordingly, the application initial operation in accordance with the length of time for power-off should be performed. However, In Japanese Patent Application Laid-open No. 2002-96452, the application initial operation in accordance with the length of time for power-off dose not performed. That is, In Japanese Patent Application Laid-open No. 2002-96452, a rotating time of the application roller at the time of the return operation is set constant regardless of an elapse of time between the previous power-off and the current power-on. Accordingly, when the lapse of time is long, the viscosity of the treatment liquid on the application roller cannot be sufficiently returned only for the rotating time in some cases. On the other hand, when the lapse of time is short, the viscosity of the treatment liquid on the application roller can be sufficiently returned even though the return operation is performed for a time less than the rotating time. Therefore, in this case, the apparatus start-up is delayed by the excessive rotating time.
In the case of Japanese Patent Application No. 2002-96452, as mentioned above, the processing for reducing the viscosity of the treatment liquid (viscosity reduction processing of treatment liquid) stuck to the application roller and the like is not performed with no consideration given to the length of time during which the viscosity of the treatment liquid increases (or a degree of thickening of the treatment liquid).